Protease nexin I immunostaining in Alzheimer's disease

The amyloid plaque proteome in early onset Alzheimer's disease and Down syndrome

Amyloid plaques contain many proteins in addition to beta amyloid (Aβ). Previous studies examining plaque-associated proteins have shown these additional proteins are important; they provide insight into the factors that drive amyloid plaque development and are potential biomarkers or therapeutic targets for Alzheimer's disease (AD). The aim of this study was to comprehensively identify proteins that are enriched in amyloid plaques using unbiased proteomics in two subtypes of early onset AD: sporadic early onset AD (EOAD) and Down Syndrome (DS) with AD. We focused our study on early onset AD as the drivers of the more aggressive pathology development in these cases is unknown and it is unclear whether amyloid-plaque enriched proteins differ between subtypes of early onset AD. Amyloid plaques and neighbouring non-plaque tissue were microdissected from human brain sections using laser capture microdissection and label-free LC-MS was used to quantify the proteins present. 48 proteins were consistently enriched in amyloid plaques in EOAD and DS. Many of these proteins were more significantly enriched in amyloid plaques than Aβ. The most enriched proteins in amyloid plaques in both EOAD and DS were: COL25A1, SMOC1, MDK, NTN1, OLFML3 and HTRA1. Endosomal/lysosomal proteins were particularly highly enriched in amyloid plaques. Fluorescent immunohistochemistry was used to validate the enrichment of four proteins in amyloid plaques (moesin, ezrin, ARL8B and SMOC1) and to compare the amount of total Aβ, Aβ40, Aβ42, phosphorylated Aβ, pyroglutamate Aβ species and oligomeric species in EOAD and DS. These studies showed that phosphorylated Aβ, pyroglutamate Aβ species and SMOC1 were significantly higher in DS plaques, while oligomers were significantly higher in EOAD. Overall, we observed that amyloid plaques in EOAD and DS largely contained the same proteins, however the amount of enrichment of some proteins was different in EOAD and DS. Our study highlights the significant enrichment of many proteins in amyloid plaques, many of which may be potential therapeutic targets and/or biomarkers for AD.

Plasminogen activator activity is inhibited while neuroserpin is up-regulated in the Alzheimer disease brain

Amyloid-beta plaques are a pathological hallmark of Alzheimer's disease. Several proteases are known to cleave/remove amyloid-beta, including plasmin, the product of tissue plasminogen activator cleavage of the pro-enzyme plasminogen. Although plasmin levels are lower in Alzheimer brain, there has been little analysis of the plasminogen activator/plasmin system in the brains of Alzheimer patients. In this study, zymography, immunocapture, and ELISAs were utilized to show that tissue plasminogen activator activity in frontal cortex tissue of Alzheimer patients is dramatically reduced compared with age-matched controls, while tissue plasminogen activator and plasminogen protein levels are unchanged; suggesting that plasminogen activator activity is inhibited in the Alzheimer brain. Analysis of endogenous plasminogen activator inhibitors shows that while plasminogen activator inhibitor-1 and protease nexin-1 levels are unchanged, the neuroserpin levels are significantly elevated in brains of Alzheimer patients. Furthermore, elevated amounts of tissue plasminogen activator-neuroserpin complexes are seen in the Alzheimer brain, and immunohistochemical studies demonstrate that both tissue plasminogen activator and neuroserpin are associated with amyloid-beta plaques in Alzheimer brain tissue. Thus, neuroserpin inhibition of tissue plasminogen activator activity leads to reduced plasmin and may be responsible for reduced clearance of amyloid-beta in the Alzheimer disease brain. Furthermore, decreased tissue plasminogen activator activity in the Alzheimer brain may directly influence synaptic activity and impair cognitive function.

Structure and function of amyloid in Alzheimer's disease

This review is focused on the structure and function of Alzheimer's amyloid deposits. Amyloid formation is a process in which normal well-folded cellular proteins undergo a self-assembly process that leads to the formation of large and ordered protein structures. Amyloid deposition, oligomerization, and higher order polymerization, and the structure adopted by these assemblies, as well as their functional relationship with cell biology are underscored. Numerous efforts have been directed to elucidate these issues and their relation with senile dementia. Significant advances made in the last decade in amyloid structure, dynamics and cell biology are summarized and discussed. The mechanism of amyloid neurotoxicity is discussed with emphasis on the Wnt signaling pathway. This review is focused on Alzheimer's amyloid fibrils in general and has been divided into two parts dealing with the structure and function of amyloid.

Increased expression and localization of a serine protease inhibitor, protease nexin-1 (PN-1), in the ovary and uterus during implantation in rat

Protease nexin-1 (PN-1) is a serine protease inhibitor (serpin) that inactivates several proteases, including thrombin, urokinase, plasminogen activators (PA), and plasmin. It also plays a role in regulating proteolytic activity generated by PA system. PN-1 is known to be involved in tissue remodeling, cellular invasiveness, matrix degradation, and tumor growth. However, the role of PN-1 in female reproductive tracts, such as the uterus, ovary, and oviduct, during pregnancy is not known. The present study was designed to investigate the changes of PN-1 mRNA level and localization in the tracts during implantation and early pregnancy by using reverse transcription (RT)-polymerase chain reaction (PCR) and in situ hybridization. We found that PN-1 mRNA levels were coordinately regulated during early pregnancy in a stage- and tissue-specific manner, such that an increased expression of PN-1 gene appeared at the time of the implantation period in the uterus and ovary. Both the uterus and ovary synthesized PN-1 mRNA and their maximal PN-1 expression occurred on Day 6.5 postcoitum (p.c.). On 13.5 days of pregnancy, PN-1 level was low in the uterus and ovary. On the other hand, PN-1 mRNA in the oviduct did not show after 6.5 days of pregnancy. It appears that PN-1 mRNA in the uterus and ovary was highly regulated during early pregnancy, which might have an important role in implantation of rat blastocysts. PN-1 was localized in endometrial stromal cells of the uterus and in granulosa cells of the unstimulated primary follicles in the ovary during periimplantation period. Also, PN-1 mRNA expression was higher at implantation period than that at nonimplantation period of pregnancy. In conclusion, PN-1 is expressed in female reproductive tracts and highly regulated during implantation and early pregnancy.

Mechanism of thrombin clearance by human astrocytoma cells

Astroglial cells secrete a variety of factors that contribute to the regulation of neurite initiation and continued outgrowth, among them proteases and protease inhibitors. An alteration in the balance between these proteins has been implicated in Alzheimer's disease, resulting in an accumulation of thrombin:protease nexin 1 (PN1) complexes in the brains of these patients. This report aims at providing a biochemical explanation for this phenomenon. We show that human astrocytoma cells bind and internalize thrombin and thrombin:PN1 complexes efficiently by a PN1-dependent mechanism. Binding was potently inhibited by soluble heparin and did not occur with the mutant PN1 (K7E) deficient in heparin binding. Receptor-associated protein, an antagonist of the low-density lipoprotein receptor-related protein (LRP), inhibited internalization of thrombin by the astrocytoma cells, but did not affect cell-surface binding. The results are consistent with a mechanism by which astrocytoma cells clear thrombin in a sequential manner: thrombin is first complexed with PN1, then bound to cell-surface heparins, and finally internalized by LRP. This mechanism provides a link between the neuronal growth regulators thrombin and PN1 and proteins genetically associated with Alzheimer's disease, such as LRP.

Serpin=serine protease-like complexes within neurofilament conglomerates of motoneurons in amyotrophic lateral sclerosis

Neurofilamentous conglomerates (NfCg), as axonal spheroids or conglomerates in motoneurons, are the histopathologic hallmarks for early stages of amyotrophic lateral sclerosis (ALS). We hypothesize that NfCg may be formed by post-translational modifications of altered Nf proteins that include: (1) hyperphosphorylation, (2) glycosylation (or glycoxidation), (3) nitration, (4) ubiquitination and/or (5) crosslinking by the Ca++-dependent transglutaminase (TGase). These, as well as other changes, are predicted to be initiated or accentuated by oxidative damage. The damaged Nf proteins then activate cascades of intracellular protein degradation which include ATP-dependent ubiquitin/proteasome proteolysis. Other proteolytic systems, either Ca++-dependent or independent, may also be activated, such as serine and cysteine protease systems. These enzymes, either lysosomal or non-lysosomal may also participate in the degradation of damaged Nf proteins being balanced by their cognate inhibitors. Protein complexes formed by these protease=inhibitor systems, along with damaged Nf proteins, may accumulate within the cell bodies as neuronal inclusions, since a number of intracellular inclusions are found in motor neurons in ALS. In the current study, we investigated the involvement of serine proteases and their serpins in NfCg formation. Pairs of three serine proteases (trypsin, chymotrypsin and thrombin) and their cognate serpins (alpha1-anti-trypsin, alpha1-anti-chymotrypsin, and protease nexin I) were probed in motoneurons with their antibodies for both NfCg and inclusions. Positive immunoreactivities for all serine proteases and their cognate serpins support the contention that the imbalance of serine proteases and internalized serpins may have a role in formation of NfCg and inclusions, and hence, the pathogenesis of ALS.

The role of the amyloid protein precursor (APP) in Alzheimer's disease: does the normal function of APP explain the topography of neurodegeneration?

Alzheimer's disease (AD) is the most common form of dementia in the aged population. Early-onset familial AD (FAD) involves mutations in a gene on chromosome 21 encoding the amyloid protein precursor or on chromosomes 14 or 1 encoding genes known as presenilins. All mutations examined have been found to increase the production of amyloidogenic forms of the amyloid protein (A beta), a 4 kDa peptide derived from APP. Despite the remarkable progress in elucidating the biochemical mechanisms responsible for AD, little is known about the normal function of APP. A model of how APP and A beta are involved in pathogenesis is presented. This model may explain why certain neuronal populations are selectively vulnerable in AD. It is suggested that those neurons which more readily undergo neuritic sprouting and synaptic remodelling are more vulnerable to A beta neurotoxicity.

Sympathetic neurite outgrowth is greater on plaque-poor vs. plaque-rich regions of Alzheimer's disease cryostat sections

Senile plaques are a characteristic histopathological feature of Alzheimer's disease (AD) and are associated with altered neuritic morphology. Numerous individual plaque components, most notably beta-amyloid, have been studied for their possible effects on neurite outgrowth in culture. However, the effect of senile plaques on neuronal morphology and function is difficult to assess. In the present study, the effect of senile plaques on neurite outgrowth was studied by culturing embryonic chick sympathetic neuronal explants on Alzheimer's tissue sections. Explants were cultured for 3 days on amygdala tissue sections from AD as well as non-AD patients in serum-free medium. Neurite outgrowth on plaque-rich regions was compared with outgrowth on plaque-poor regions of the same tissue section, and with outgrowth on non-AD tissue, through colocalization of the living explants and the underlying plaques. Explants growing on plaque-rich regions showed significantly less neurite outgrowth compared with those on plaque-poor regions in the same section or on control brain tissue. These results suggest that plaques are poor substrates for neurite outgrowth as compared with non-plaque areas of the same tissue sections, and support the hypothesis that components of the senile plaques may inhibit neurite outgrowth.

Butyrylcholinesterase in the life cycle of amyloid plaques

Deposits of diffuse beta-amyloid (Abeta) may exist in the brain for many years before leading to neuritic degeneration and dementia. The factors that contribute to the putative transformation of the Abeta amyloid from a relatively inert to a pathogenic state remain unknown and may involve interactions with additional plaque constituents. Matching brain sections from 2 demented and 4 nondemented subjects were processed for the demonstration of Abeta immunoreactivity, butyrylcholinesterase (BChE) enzyme activity, and thioflavine S binding. Additional sections were processed for the concurrent demonstration of two or three of these markers. A comparative analysis of multiple cytoarchitectonic areas processed with each of these markers indicated that Abeta plaque deposits are likely to undergo three stages of maturation, ie, a "diffuse" thioflavine S-negative stage, a thioflavine S-positive (ie, compact) but nonneuritic stage, and a compact neuritic stage. A multiregional analysis showed that BChE-positive plaques were not found in cytoarchitectonic areas or cortical layers that contained only the thioflavine S-negative, diffuse type of Abeta plaques. The BChE-positive plaques were found only in areas containing thioflavine S-positive compact plaques, both neuritic and nonneuritic. Within such areas, almost all (>98%) BChE-containing plaques bound thioflavine S, and almost all (93%) thioflavine S plaques contained BChE. These results suggest that BChE becomes associated with amyloid plaques at approximately the same time that the Abeta deposit assumes a compact beta-pleated conformation. BChE may therefore participate in the transformation of Abeta from an initially benign form to an eventually malignant form associated with neuritic tissue degeneration and clinical dementia.

Sprouting and abnormal contacts of nonmedullated axons, and deposition of extracellular material induced by the amyloid precursor protein (APP) and other protease inhibitors

We have reported that the local administration of serine protease inhibitors (amyloid precursor protein with the Kunitz insert (APP K+), aprotinin, and leupeptin) to the rat sciatic nerve determines a sprouting response of myelinated axons, proliferation of Schwann cells, and demyelination, 5 to 7 days later. Further study of these nerves with the electron microscope revealed (i) a sprouting response of nonmedullated axons, (ii) the appearance of fine axons with a few turns of compact myclin, (iii) abnormal contracts of axons with basal laminae, with fibroblast-like cells, and between them, (iv) the occurrence of hemidesmosome- and desmosome-like junctions between Schwann cell processes, and between Schwann cells and axons, and (v) the appearance of amorphous and fibrillary extracellular deposits alongside the axolemma. The adjacent proximal and distal segments were normal, i.e., axons remained continuous, and the alterations were confined to the segment exposed to the protease inhibitors. Heated APP Kappa +, APP without the Kunitz insert (APP K-), bovine serum albumin, and saline, did not elicit cytological alterations. Our results suggest that these inhibitors of serine proteases (i) set free a sprouting drive of axons by disrupting an ongoing repressive mechanism: (ii) modify the adhesive properties of axons and Schwann cells, and (iii) alter the natural history of an extracellular material. The imbalance of an extracellular protease system may participate in the pathogenesis of Alzheimer's disease.

Complement activation in amyloid plaques in Alzheimer's disease brains does not proceed further than C3

In Alzheimer's disease (AD) patients, the complement components Clq, C4 and C3 can be detected in different types of beta/A4 plaques, one of the hallmarks of AD. Contradictory findings on the presence of late complement components in AD brains have been reported. Nevertheless, it was suggested in recent studies that in AD brain complement activation results in complement membrane attack complex (MAC) formation and that complement activation may act as an intermediate between beta/A4 deposits and the neurotoxicity observed in AD. In the present study the presence of a number of complement components and regulatory proteins in AD temporal cortex and, for comparison, in glomerulonephritis (GN) was analysed. In GN kidneys, besides Clq, Clr, Cls and C3, the late components and the C5b-9 complex are also associated with capillary basement membrane and mesangial immune complex deposits. In AD temporal cortex Clq, C4 and C3 are co-localized with beta/A4 deposits. However, in contrast to the GN kidney, the late complement components C5, C7 and C9, as well as the C5b-9 membrane attack complex cannot be detected in beta/A4 positive plaques. The absence of the cytolytic C5b-9 complex in AD brain suggests that in AD, the complement MAC does not function as the proposed inflammatory mediator between beta/A4 deposits and the neurofibrillary changes.

Butyrylcholinesterase reactivity differentiates the amyloid plaques of aging from those of dementia

In a sample of consecutively received, 4 demented and 4 age-matched nondemented brains, the total cortical area covered by plaque-like A beta amyloid and butyrylcholinesterase deposits was measured at two regions of the temporal cortex with the help of computed densitometry. Demented as well as age-matched nondemented brains contained A beta and butyrylcholinesterase-positive plaques. The total cortical area covered by the A beta precipitates was higher in demented individuals but there was overlap with the values seen in the specimens from nondemented individuals. The proportional plaque area displaying butyrylcholinesterase reactivity was very significantly and five fold to sixfold higher in the demented than in the nondemented group and there was no overlap between the two populations. Diffuse A beta deposits in nondemented elderly brains may represent a benign or preclinical stage of plaque deposition with relatively little pathological effect on brain tissue and mental function. Our results suggest that the progressively more extensive butyrylcholinesterase reactivity of plaques may participate in their transformation from a relatively benign form to pathogenic structures associated with neuritic degeneration and dementia.

Neuronal expression of protease-nexin 1 mRNA in rat brain

Protease-nexin 1 (PN1), also known as glia-derived nexin, is a protease inhibitor secreted by cultured fibroblasts and glioma cells, with postulated roles in regeneration and the regulation of neurite outgrowth. In this study we have localised the sites of PN1 gene expression in rat brain using in situ hybridisation. As expected, cultured cortical astrocytes contained relatively high levels of PN1 mRNA. However, the mRNA localisation in rat brain suggested that the primary sites of synthesis in the CNS are neuronal. Relatively high levels of PN1 mRNA were found in the olfactory nerve layer of the olfactory bulb, in layer V of the cerebral cortex, in magnocellular neurones of the basal forebrain, and in scattered neurones of the striatum. The results show that PN1 gene expression occurs in discrete populations of neurones in the brain, and suggest that these neurones may therefore play a role in the local regulation of neurite outgrowth.

Morphological and biochemical analyses of amyloid plaque core proteins purified from Alzheimer disease brain tissue

Amyloid plaque cores were purified from Alzheimer disease brain tissue. Plaque core proteins were solubilized in formic acid which upon dialysis against guanidinium hydrochloride (GuHCl) partitioned into soluble (approximately 15%) and insoluble (approximately 85%) components. The GuHCl-soluble fraction contained beta-amyloid1-40, whereas the GuHCl-insoluble fraction was fractionated into six components by size exclusion HPLC: S1 (> 200 kDa), S2 (200 kDa), S3 (45 kDa), S4 (15 kDa), S5 (10 kDa), and S6 (5 kDa). Removal of the GuHCl reconstituted 10-nm filaments composed of two intertwined 5-nm strands. Fractions S5 and S6 also yielded filamentous structures when treated similarly, whereas fractions S1-S4 yielded amorphous aggregates. Chemical analysis identified S4-S6 as multimeric and monomeric beta-amyloid. Immunochemical analyses revealed alpha 1-antichymotrypsin and non-beta-amyloid segments of the beta-amyloid precursor protein within fractions S1 and S2. Several saccharide components were identified within plaque core protein preparations by fluorescence and electron microscopy, as seen with fluorescein isothiocyanate- and colloidal gold-conjugated lectins. We have shown previously that this plaque core protein complex is more toxic to neuronal cultures than beta-amyloid. The non-beta-amyloid components likely mediate this additional toxicity, imposing a significant influence on the pathophysiology of Alzheimer disease.

The influence of denervation on beta-amyloid protein precursor and alpha 1-antichymotrypsin in mouse skeletal muscle

A serpin, alpha 1-antichymotrypsin (alpha 1-ACT), and Kunitz inhibitor containing forms of the beta-amyloid precursor protein (beta APP) may be important components of the balance between serine proteases and inhibitors in the nervous system. In the current report we studied whether axotomy affected the localization of beta APP and alpha 1-ACT in adult mouse muscle. Immunocytochemical experiments indicated that beta APP was present in normal muscle both at neuromuscular junctions and within intramuscular nerves. alpha 1-ACT was also present at neuromuscular junctions, on the perineurium of nerves and endothelial cell surfaces. Following axotomy, both beta APP and alpha 1-ACT disappeared from intramuscular nerves simultaneously. However, at the neuromuscular junction alpha 1-ACT decreased more rapidly with beta APP lingering before disappearing.

alpha 2-Macroglobulin expression in neuritic-type plaques in patients with Alzheimer's disease

Because it has been suggested that alpha 2M could be involved in the generation of amyloid peptide, attention was given to a possible association of alpha 2M expression and amyloid accumulation in the brain. Therefore, we investigated the presence of the proteinase inhibitor alpha 2-macroglobulin (alpha 2M) in the cerebra of 4 patients with Alzheimer's Disease (AD). One case of a patient with Down's syndrome, 2 cases of patients with Dementia of the Lewy Body type (DLB), 1 case of an aged, clinically nondemented person who displayed many amyloid plaques, and 3 normal aged control brains were also studied. The results obtained by immunocytochemistry with monoclonal antibodies directed against two different epitopes of human alpha 2M showed an association of alpha 2M, only with neuritic-type plaques in patients with AD. No alpha 2M immunoreactivity was found in either preamyloid-type plaques or burned out-type plaques in AD, DLB, or aged nondemented controls. The results do not support a direct role of this proteinase inhibitor in the formation of amyloid. Because alpha 2M is observed to be associated with reactive microglia in the outer border of the neuritic plaques, the data suggest that alpha 2M could be a marker for an inflammatory cellular process in these neuritic plaques.

The glia-derived protease nexin 1 persists for over 1 year in rat brain areas selectively lesioned by transient global ischaemia

The re-expression of the developmentally regulated serine protease inhibitor glia-derived nexin (GDN) was investigated 1 year after transient global ischaemia induced by the four-vessel occlusion technique in rats. The CA1 sector of the hippocampus was severely shrunken due to the absence of pyramidal cells, but still clearly discernible due to the continued presence of the parvalbumin-containing GABAergic neurons. In this partially neuron-depleted hippocampus, GDN immunoreactivity was found in reactive astrocytes containing glial fibrillary acidic protein. GDN-positive astrocytes were also found in other lesioned areas, the reticular thalamic nucleus and the cerebellar cortex. Thus, the re-expression of GDN in the adult excitotoxically lesioned brain described previously in the gerbil model of ischaemia persists. The continued presence of the protease inhibitor might disturb the proteolytic balance and lead to the deposition of pathological breakdown products of proteins, e.g. beta-amyloid.

Plasminogen activator inhibitor 1, the primary regulator of fibrinolysis, in normal human cerebrospinal fluid

The occurrence of type-1 plasminogen activator inhibitor (PAI-1) in human cerebrospinal fluid (CSF) has not previously been reported. As a member of the serpin superfamily of serine protease inhibitors and an acute phase response component, PAI-1 has powerful potential roles in nervous system homeostasis. We have detected this serpin antigen using a polyclonal anti-PAI-1 antibody in normal human CSF. In Western blotting, PAI-1 in several CSF samples appears as a two-band antigen of Mr = 54 and 35 kDa, presumably the intact and proteolytic fragment, respectively. In vitro complex formation studies confirm that the 54 kDa form of PAI-1 interacts with 125I-urokinase after activation with SDS, but the 35 kDa form does not. Quantification of total PAI-1 antigen in 18 normal human CSF samples by ELISA reveals a mean value of 1.0 +/- 0.07 (SEM) micrograms/dL, indicating that a relatively low concentration of the inhibitor occurs in normal human CSF. This information should now allow comparison of PAI-1 levels and activity in various neurologic disorders.

Axonal sprouting induced in the sciatic nerve by the amyloid precursor protein (APP) and other antiproteases

Protease inhibition is the mechanism by which some trophic factors promote the extension of neurites. In the rat sciatic nerve, we assessed the ability to induce sprouts of the APP isoform that embodies the Kunitz antiprotease domain and other antiproteases. With the electron microscope, axonal sprouts were found when antiproteases were supplied but not after administration of inactive substances. We conclude that axons have a drive to sprout which can be released by the unbalance of an extracellular protease-antiprotease system. We propose that this system is involved in the pathogenesis of Alzheimer's disease.

Laminin and its neurite outgrowth-promoting domain in the brain in Alzheimer's disease and Down's syndrome patients

Immunocytochemistry, radioimmunoassay, immunoblotting, Northern analysis, and polymerase chain reaction (PCR) technique were applied to investigate the distribution of laminin and its neurite outgrowth domain in brains of neuropathologically verified cases of Alzheimer's disease and Down's syndrome. New antibodies against a neurite outgrowth domain of laminin were characterized and were used in localization of this peptide antigen in the human brain. Laminin was found as large punctate deposits in all plaques in the affected brains. Laminin synthesis was increased as assessed by RNA blotting and immunoblotting, and glial cells were heavily immunoreactive with antibodies for a neurite outgrowth-promoting peptide antigen of the B2 chain of laminin. This peptide antigen not only was produced by glial cells but also was deposited in the brain tissue. As this peptide antigen promotes neurite outgrowth at low concentrations, and is specifically neurotoxic at high concentrations, it may play a synergistic role with other molecules in inducing the sprouting and neurodegeneration occurring in brains of patients with either Alzheimer's disease or Down's syndrome.

Casein kinase II is associated with neurofibrillary tangles but is not an intrinsic component of paired helical filaments

Neurofibrillary tangles (NFT) are pathological cytoskeletal structures composed of paired helical filaments (PHF), and are found in neurons of patients afflicted with many neurodegenerative disorders, including Alzheimer's disease (AD). We previously found that an antiserum against casein kinase II (CK-II) stained NFT intensely in the brain tissue of AD patients. In the current study, we found that the anti-CK-II antiserum stains NFT and neuronal inclusions in many other neurodegenerative diseases as well, including Guam-Parkinson dementia complex, chromosome 18 deletion syndrome, progressive supranuclear palsy, Kufs' disease, and Pick's disease. This antiserum reacted, in crude brain homogenates, with both a doublet of Mr 43,000 and a Mr 27,000 Da protein which could correspond to the alpha, alpha', and beta chains of CK-II. The staining of these bands was adsorbed by preincubating anti-CK-II antiserum with purified CK-II. Preincubation of brain sections with purified CK-II strongly intensified the immunostaining of NFT with anti-CK-II, suggesting that NFT may bind CK-II. In the AD brain homogenates, the particulate CK-II levels are increased whereas the cytosolic levels are decreased without a change in total CK-II levels, consistent with the idea that CK-II binds to the particulate PHF, a major constituent of NFT. In accord with these findings, purified PHF bound CK-II, but purified PHF did not contain CK-II as its component. These results suggest that CK-II might be an extraneously deposited component of NFT. Thus, the altered CK-II compartmentalization might have significant consequences in the pathogenesis of AD.

Neurite outgrowth on postmortem human brain cryostat sections: studies of non-Alzheimer's and Alzheimer's tissue

An in vitro assay to test for regional differences in neurite growth-promoting and growth-inhibiting factors in tissue sections of CNS tissue has been adapted to the use of postmortem human brain tissue. Frozen sections of the temporal lobe from victims of Alzheimer's disease were used as substrates for sympathetic neurite outgrowth in tissue culture. Tissue sections from a non-Alzheimer's brain were used as a control. Both explanted chick sympathetic ganglia and dissociated chick sympathetic neurons were cultured for 3 to 5 days on tissue sections in the presence of exogenous nerve growth factor. The dichotomy between gray and white matter portions of the tissue sections in supporting neurite outgrowth that was previously reported for fresh frozen human brain tissue was also found to persist in postmortem tissue. In addition, the total neurite outgrowth from explanted sympathetic ganglia was found to be significantly less on postmortem sections when compared with previous results obtained from fresh frozen tissue samples of epileptic tissue. Dissociated neurons exhibited neurite outgrowth on Alzheimer's sections that showed preferential growth on blood vessel segments but no affinity for senile plaques. The results suggest that there is some decline in the neurite growth-promoting ability of cortical gray matter obtained from postmortem-derived brains when compared with fresh tissue and that senile plaques do not represent sites of neurite stimulation in this in vitro system.

Effects of injected Alzheimer beta-amyloid cores in rat brain

Although amyloid deposits have long been known to accumulate in Alzheimer disease (AD) brain, their origin and significance remain speculative. Because of the lack of an in vivo model where amyloid deposits can be induced, the relationship of the extracellular beta-amyloid deposits to other AD pathology has never been directly investigated. Therefore, we injected SDS-isolated amyloid cores into rat cortex and hippocampus. Similarly isolated lipofuscin fractions from control human brains were injected on the contralateral side. Rats were perfused and brains were examined immunohistochemically at 2 days, 7 days, and 1 month after injection. Alz-50, a monoclonal antibody against abnormally phosphorylated tau proteins, stained neurons along the cortical needle track at 2 but not 7 days after injection of either amyloid or lipofuscin. At 1 month, however, ubiquitin, Alz-50 antigen, and silver-positive structures were observed only in response to amyloid. In 7 of 10 animals, there was considerable neuronal loss in the hippocampal layers. In each instance, these effects were in the immediate vicinity of beta-protein immunoreactive material. Marked neuronal loss was never observed at any time after lipofuscin injection. These results indicate a neuronal response to amyloid. When preparations of mature plaque amyloid isolated from the AD brain are injected into the rat brain, they exert neurotoxic effects and induce antigens found in the AD brain.

Protease nexin-1 activity in cultured Schwann cells

We report that protease nexin-1 (PN-1), a serine protease inhibitor known to have neurite-promoting effects, is made by Schwann cells in tissue culture. Three modalities have been used to demonstrate the presence of PN-1 in Schwann cell cultures. Immunostaining of the cultures with anti-PN-1 antibody gives positive staining over cells and matrix. Western blots of Schwann cell conditioned medium (CM) using anti-PN-1 antibody show a band that co-migrates with the PN-1 standard at 45 kDa. Biochemical assay for protease inhibitory activity shows that CM inhibits thrombin activity in a calorimetric assay. The CM-mediated inhibition of thrombin is reversed if the CM is pre-incubated with anti-PN-1 antibody.

Plasminogen activators and inhibitors in the neuromuscular system: III. The serpin protease nexin I is synthesized by muscle and localized at neuromuscular synapses

Recent studies suggest that the nature of events leading to the formation, maintenance, and elimination of synapses may be regulated by cascade-type, locally expressed proteases and protease inhibitors acting on adhesive extracellular matrix components. We have identified a molecule in conditioned medium of murine skeletal muscle cells that in molecular weight, target protease inhibition, heparin-binding and cross-reactivity with authenic antisera is similar to the human serine proteinase inhibitor, protease nexin I. Protease nexin I is a 43-50 kDa glycoprotein of the serpin superfamily (arg-serpin class). Purified anti-protease nexin I antibody (anti-47 kDa) stains adult mouse skeletal muscle in discrete foci that precisely superimpose on synaptic neuromuscular junctions. Protease nexin I appears in patches on surfaces of cultured mouse skeletal myotubes, but not on myoblasts. These patches co-localize with acetylcholine receptor clusters and acetylcholinesterase staining during cellular maturation in culture. Evidence that protease nexin I is a synaptic, extracellular antigen is particularly intriguing since it has been shown to be identical, in structure and activity, with a factor released by glial cells, called glia-derived nexin that stimulates mouse neuroblastoma cell neurite outgrowth and inhibits granule cell migration. Protease nexin I inhibits both tumor cell and myoblast plasminogen activator-mediated destruction of extracellular matrix. Thus, such observations as presented in this report provide further evidence for involvement of cascade proteolytic systems, and their post-translational regulation by specific serpins, in the remodeling that occurs in synapse formation and elimination.

The binding of basic fibroblast growth factor to Alzheimer's neurofibrillary tangles and senile plaques

Brain sections from Alzheimer's disease (AD) patients and controls were treated with basic fibroblast growth factor (bFGF) and then immunostained with anti-bFGF. Additional sections were treated with biotinylated bFGF without using the anti-bFGF. Labelling was visualized by the ABC method. Both protocols above intensely labelled neurofibrillary tangles, senile plaques and amyloidotic vessels in AD brains. Omission of the bFGF treatment abolished the staining of the AD lesions. The pretreatment of sections with heparitinase also reduced their staining. These results indicate that AD lesions contain bFGF-binding sites and that the chemical substrate for bFGF binding to AD lesions was heparan sulfate.

Antibodies to fibronectin bind to plaques and other structures in Alzheimer's disease and control brain

Antibodies to fibronectin (Fn) bind not only the basal lamina in Alzheimer's disease brain, but also crystal-like formations in the grey matter, senile plaques, a subset of neuronal perikarya, and large highly processed stellate formations which were both neurofilament and glial fibrillary acidic protein (GFAP) negative and which were identified at a lower frequency in non-demented control brains.